Poly(vinyl alcohol) and its copolymers are known to possess low permeabilities to gases. However, the use of these materials for packaging in their native form restricts their use in moisture-containing atmospheres due to the presence of the many hydroxyl groups in the polymer. Further, permeabilities to oxygen, carbon dioxide and other fixed gases are very low, and increase exponentially as a function of the relative humidity. Polyolefin copolymers exhibit the sensitivity to humidity to a lesser degree. Commercial packaging and other barrier materials require low permeabilities to gases and moisture. A recent proposal to overcome this problem was disclosed in U.S. Pat. No. 4,003,963 by using certain mixtures of poly(vinyl chloride) and poly(vinyl alcohol) copolymers. The vinyl chloride polymer containing no carboxyl groups was blended with about 10-30 percent by weight, based on the weight of vinyl chloride polymer, of an ethylene/vinyl alcohol copolymer containing greater than about 61 weight percent or 50 mole percent of vinyl alcohol as comonomer.
Another approach to the problem is disclosed in U.S. Pat. No. 3,585,177. According to this patent, a lower alpha olefin/vinyl alcohol copolymer is prepared having a residual ester content below 3 percent and an olefin content between 5 and 40 percent by weight. Differential thermal analysis was used to show that the copolymers have a single narrow endotherm with a melting range of less than 30.degree. C. Other combinations in the art of barrier compositions are blends of inexpensive materials with those materials having good barrier properties. Such possibilities are limited by the incompatibilities of such blends.